REPORT OF THE DIRECTOR I918 I5I 



Rust, of Ordovician age. On slide i, for example, a few circular 

 openings occur in a colloidal base, but not enough is preserved to 

 determine whether they belong to the Spinnellarian or Nasselarian 

 group. 



Radiolaria belong to very deep water; but they occur to a limited 

 extent in all oceans where the salinity is not too low, in shallow as 

 well as deep water, so that their presence in these cherts does not 

 require an abyss of 2 miles depth to account for their occurrence. 

 They never had an extensive development, however, until Miocene 

 time, but their skeletons have been preserved in the oldest fossil- 

 iferous horizons. We believe the radiolarian in the chert was of 

 spherical form and that the uneven distribution and unequal spacing 

 of the large pores (some 0.025 mm in diameter) is due to tangential 

 cutting of a sphere. As far as this unsatisfactory evidence goes it 

 seems to indicate Lower Silurian age. 



Evidence from Bryozoa 



An eight-lobed star-shaped fragment occurs on slide 6 (poorly 

 on slide i), which does not belong to the Foraminif era ; but we believe 

 it represents the zooecia of a bryozoan-like Arthroclema cut in trans- 

 verse section.^ Both Arthroclema and Helopora would show such 

 lobate structure but we do not know whether an eight-lobed form 

 could be obtained from these. From illustrations given, the number 

 of lobes does not seem to be constant, for some show six and others 

 seven of such zooecial segmentations. One or two additional bryo 

 zoan-like forms occur. On slide 4 occurs a bryozoan section which 

 seems to me to be related toHomotrypa similis Foord 

 found in the Cambro-Silurian rocks of Canada. It is so cut that no 

 focus can be had which brings out its exact structure. In addition 

 we have a few surface apertures in fragmentary masses present, but 

 in no case can we determine the species to which these Bryozoa 

 belong. We believe, however, that such evidence as can be obtained 

 from a further study of these forms will result in indicating their 

 Lower Silurian age. 



Evidence from Additional Organisms 



Several problematical specimens occur on the slides which ought 

 to be included in this survey, even though it is impossible to 

 determine their character. Some of these may be diatoms like 

 the oval, lenticular specimen seen on slide 6 and many others, but we 



^Ulrich, Silurian Bryozoa, Geol. Minn., v. 3, pt i, 1895, pi. II, figs. 13-15, and 

 23, 24, 28 and 29. 



